Various industrial processes may require a continuous flow of liquids or gases. These materials are commonly supplied from a source via conduit, such as low or high pressure piping. If an emergency situation arises, an immediate shutdown of the flow of such materials may be required—particularly (although not exclusively) in the case of flammable, explosive or otherwise hazardous materials.
An emergency shutdown valve is typically installed in a conduit that carries liquids or gases in a given facility. In the case of an emergency shutdown situation, the emergency shutdown valve must reliably cutoff the flow of material. Depending on the applicable safety requirements, such shutdown valves must typically operate to cut off the flow with a probability of failure of less than 10−3-10−9.
Under normal operating conditions, a continuous flow of material through a given conduit and its associated emergency shutdown valve(s) may be maintained without any interruptions for a relatively long period of time. For example, a given shutoff valve may not be used for several years or may never be used for its intended purpose.
Consequently, safety precautions generally dictate and applicable government agencies normally require companies to test their emergency shutdown valves on a regular basis in order to ensure that the emergency shutdown valves will operate properly if an emergency shutdown situation actually arises. As should be apparent to one of skill in the art, this mandatory testing of emergency shutdown valves is desirable for a number of reasons. First, such testing ensures that the emergency shutdown valves themselves are not defective and will move and otherwise function as expected. Testing is also desirable because material may flow through the valves under extreme conditions such as high or low temperatures and high pressures, and testing may expose defects or other problems that could lead to valve failure when subjected to such conditions. Additionally, the material flowing through the valves may also comprise chemically aggressive media that can produce condensate bumps, corrosion, and/or defects inside the associated conduit that can block emergency shutdown valves and lead to catastrophic results. Consequently, regular valve testing may also help to reveal such conditions before they can adversely affect valve operation.
Therefore, entities such as industrial companies, etc., that have facilities where emergency shutdown valves are present, routinely test the emergency shutdown valves for proper operation as required by law or possibly more frequently as dictated by internal safety standards. The interval of such scheduled emergency shutdown valve testing is commonly much shorter than several years, and may be even more frequent.
A common and major problem associated with the testing of emergency shutdown valves is the very stoppage of flow that the valves are designed to produce. That is, while it is obviously required that an emergency shutdown valve stop a flow of material in a true emergency shutdown situation, testing often occurs when a facility would otherwise be operating normally and where stopping the flow of a needed material is undesirable. As a result, valuable production time may be lost as a result of testing an emergency shutdown valve. Because emergency shutdown valves are often present in large-scale industrial manufacturing processes, this lost production may be associated with significant lost revenue.
The aforementioned and disadvantageous loss of production resulting from emergency shutdown valve testing may be exacerbated due to the inert nature of many industrial processes, which require time to stop and restart. As a result, it is not uncommon for a given facility to lose several hundred thousand dollars in production in order to adequately test an emergency shutdown valve.
In light of this problem, there has been a search for a technique of testing emergency shutdown valves that does not require the interruption of an associated industrial (e.g., manufacturing) process. In this regard, it has become known to design material transport systems having duplicative (redundant) emergency shutdown valves. In such a system, a given flow of material may be split into two conduits, each having its own emergency shutdown valve. Consequently, only one emergency shutdown valve at a time needs to be closed during a testing operation, which allows the flow of material to continue—albeit at a reduced rate—through the other conduit and its emergency shutdown valve. Once testing is completed on the first emergency shutdown valve, the other valve may be tested in a like manner. The obvious drawback to this solution is, of course, the need to purchase a redundant emergency shutdown valve at each location where an emergency shutdown valve is needed, and the additional costs associated with splitting a given conduit into two runs and installing, maintaining and testing an extra valve.
An alternative approach has also been suggested whereby the testing process is altered rather than the material transport system. In this approach, a given emergency shutdown valve is simply closed less than completely during testing, which permits some amount of material flow to continue during the testing period. However, this approach obviously cannot ensure with required certainty that the tested emergency shutdown valve will function to completely block material flow in an emergency shutdown situation. As such, use of this technique may result in a potentially dangerous situation.
While alternative testing systems/methods have been proposed and tested, the most simple and the most commonly applied approach to emergency shutdown valve testing is still to test the valves regularly and to tolerate any resulting economic losses due to production interruptions. A better solution is needed, and such solutions are provided by the various possible embodiments of the invention.